An X-ray imaging apparatus irradiates X-rays to an object and performs fluoroscopy of the object by detecting the X-ray. The X-ray imaging apparatus is becoming pervasive. Under medical treatment in a blood vessel using the X-ray imaging apparatus, especially in a head region where the structure of the blood vessel is complicated, when a doctor sees the perspective image obtained by the fluoroscopy, a fluoroscopy roadmap, in which previously captured blood vessel image is combined with the perspective images to show combined images as a guide for the blood vessel, is widely used.
Fluoroscopy subtraction is known as one of the fluoroscopy roadmap. In the fluoroscopy subtraction, subtraction between the perspective images and a blood vessel image, etc. is performed to show a catheter or a guide wire, etc. in black in the image where the blood vessel is shown in white and a background (e.g., a bone) is deleted. In the fluoroscopy subtraction, a blood vessel image is generated by injecting contrast agents into the target blood vessel and performing fluoroscopy or capturing images. Next, a subtraction image is generated by performing, for example, subtraction between the perspective image, which can be obtained by fluoroscopy, and the blood vessel image. The generated subtraction image does not have a background (e.g., a bone) and have the blood vessel image. A doctor manipulates a catheter or a guide wire, etc., while checking a blood vessel using the subtraction image.
The fluoroscopy subtraction is indispensable to today's medical treatment with the spread of the medical treatment using a catheter in a blood vessel. Thus, various methods for generating a subtraction image have been proposed (see, Japanese Patent Publication (Kokai) No. 2002-199279).
In the above mentioned subtraction image, a background, such as a bone, which appears in a perspective image and a blood vessel image in common, disappears, and the blood vessel and the insertion instrument (e.g., a catheter inserted in an object), is displayed as a difference image. However, when the object moves in manipulation (e.g., by motion), the background position captured in the perspective image moves, and thus the moved background is displayed on a subtraction image. The object appearing in a subtraction image due to, for example, the motion of the object is called a “motion artifact.” The motion artifact hinders doctor's manipulation.
In order to reduce the motion artifact captured in the subtraction image, a blood vessel image can be recaptured for the moved object to show a subtraction image using the recaptured blood vessel image. However, the recaptured blood vessel image causes an increase in the amount of X-ray irradiation.